1. Field of the Invention
The present invention relates to a zoom lens focal point adjusting device of a camera which adjusts the position of the lenses in the optical axis direction.
2. Description of Related Art
In recent years, zoom lenses, including vari-focal photographing lenses, have included three or more lens groups, rather than two lens groups which have previously been used. The number of lens groups has been increased to meet the demand of photographers who desire a zoom camera having a high-magnification (high-zoom ratio) lens and also high performance.
Before a zoom lens type camera is completely assembled, or at least before it is put on the market, a focal point adjusting operation is often carried out, especially if the zoom camera has a high-zoom ratio. The focal point adjusting operation is effected to adjust the position of one or more of the lenses constituting the zoom lens of a zoom camera in the optical axis direction, after an in-focus state has been obtained, with respect to an object to be photographed. This operation is effected so that the in-focus state will not vary even if zooming or variation of the focal point (zooming or variation of the focal point will hereinafter be collectively referred to as zooming) is effected. This kind of focal point adjusting operation typically uses a lens supporting frame, which holds the lens of a zoom lens, and a lens frame supporting member, which is made separately from the lens supporting frame and which holds the same. The lens supporting frame and the lens frame supporting member are connected by threading. The threading permits adjustment of the relative position of the lens supporting frame and the lens frame supporting member in the optical axis direction. With this arrangement, in accordance with the threading mechanism, the lens, which is to be moved in the optical axis direction to accomplish focal point adjustment, can be continuously moved in the optical axis direction.
In a known zoom camera, having a conventional zoom lens composed of two lens groups, it is often the case that the first lens group, closest to the object side, is moved in the optical axis direction to effect a focal point adjusting operation. The first lens group is the lens group to be adjusted, since this lens group is most easily accessed. However, as for a zoom camera having a zoom lens consisting of three or more lens groups, the amount of deviation of the focal point, with respect to a unit of deviation of the first lens group in the optical axis direction, is relatively small as compared with those of the other lens groups. Therefore, when a focal point adjustment is to be executed with the focal point adjusting mechanism, by moving the first lens group in the optical axis direction, a large space must be reserved in which adjustment can be effected. In other words, the space allotment must be sufficient for the necessary adjustment, resulting in an undesirably large camera.